Centrifugal clutches are widely used in power tools and other equipment driven by internal combustion engines. For example, as applied to a chain saw, a centrifugal clutch is provided between the engine and a sprocket driving the saw chain. When the engine is running at idling speed, the clutch is disengaged so that the chain is not driven. When the engine speed is increased to a predetermined value the clutch engages to drive the saw chain. This provides convenient control of the chain and also is a safety factor in that the saw chain is not driven when the engine is started and is idling. Moreover, it reduces the starting torque on the engine.
A centrifugal clutch customarily comprises an outer drum and a rotor inside the drum. The rotor constitutes the driving member of the clutch while the drum is the driven member. The rotor usually comprises a hub or body portion at least two weights separte from and movably mounted on the body portion and one or more springs for holding the weights out of engagement with the drum when the rotor is stationary or is rotating at a speed below a selected critical speed. When the speed of rotation of the rotor is increased to a critical valve, the weights are move outwardly by centrifugal force against the action of the spring means so as to engage the drum and thereby provide a driving connection between the drum and the rotor. The manufacture and assembly of the parts comprising the rotor of a centrifugal clutch of this kind involve a considerable amount of expense. By reason of unavoidable manufacturing tolerances in the production of rotor parts it is difficult in commercial production to manufacture clutches of consistently uniform operating characteristics. Moreover, the operating characteristics of an individual clutch may change in use, for example by reason of dirt entering between the moving parts of the clutch rotor.
In U.S. Pat. No. 3,718,214 there is disclosed a centrifugal clutch comprising a clutch drum and a rotor of one piece construction. The rotor comprises a diametrically extending crossbar portion having a hub portion with a central bore, two like weight portions on diametrically opposite sides of the crossbar portion and integral thin spring portions connecting opposite ends of the crossbar portion with the respective weight portions. The one piece rotor construction disclosed in U.S. Pat. No. 3,718,214 represents an important advance over the multiple part construction of earlier centrifugal clutches.